I think obviously, a prime factor in all this, is that many of the states near the bottom with the lowest per capita car-crash deaths is a result of much of said state's population using public transportation VS personal automobiles.

DC for example ranked the lowest. DC has a highly used public trans system. Wyoming, the highest, has the lowest population density minus Alaska, an extremely remote state, absolutely no public trans network(s), rugged terrain, etc. - are obviously contributing factors.

Why Mississippi is so high, or Arkansas, that's a little more of an enigma.